The invention relates to a cost-efficient method for calibrating magnetic field sensors in a high-precision directional drilling device, for the early, reliable and timely localization of the wellbore with specification of a selectable directional path of the wellbore for deep drilling, and to a directional drilling device comprising a housing, a bit drive shaft, which rotates in the housing and bears a rotary drill bit at its end that preferably protrudes from the housing, and also comprising a control device connected to magnetic field sensors and located within the housing, and a plurality of direction control devices, located within the housing, for generating directing forces having radially alignable force components for the alignment of the directional drilling device during drilling operations.
Directional drilling is the term used for drilling methods that allow the direction of a bore to be influenced. Complex systems are used to alter and determine the path of the wellbore in any direction. Values for inclination and magnetic north, inter alia, are measured. The sensors for detecting magnetic north are placed in non-magnetizable steels at a sufficient distance from any parts that might cause magnetic interference. Only in this way can magnetic north be detected without interference and drilling routed in the proper, i.e. predefined, direction. When using directional drilling equipment, it is advantageous for the measurements of inclination and direction to be taken as close behind the bit as possible to ensure that the wellbore is following a controlled and planned desired path. In modern rotary steerable systems, only the inclination sensor is integrated directly into the system, while the direction sensors are located in a non-magnetic sector located many meters behind the system to enable magnetic north to be detected with the required accuracy. Without appropriate corrections, integrating the direction sensors and the detection of magnetic north together with the inclination sensors in the directional drilling device would result in magnetic declination and would allow major inaccuracies in direction sensing.
Conventional directional drilling devices comprise a tubular housing. The drill pipe string, also called the drill string, is accommodated inside the housing, at least in the base section thereof facing away from the rotary drill bit. The rotary drill bit is located in the head section of the housing; at least a portion of the bit drive shaft to which the rotary drill bit is coupled is likewise positioned rotatably in the head section of the housing. The base section merges into the body section of the housing, which merges into the head section. In conventional directional drilling devices, the magnetic field sensors are located in the base section of the housing, as far as possible from the head section and the body section of the housing, in an effort at least to diminish the magnetic declinations, which occur even during operation of the rotary drill bit and are generated as a result of the devices, components, etc. being built into the head section and body section of the housing, and the influence of such declinations on the magnetic field sensors by spacing or distancing the magnetic field sensors from the head section of the housing in conventional drilling devices. Despite the spatial distancing of the magnetic field sensors from the head section and body section, interference with the acquisition of position data acquired by magnetic field sensors is nevertheless manifested in conventional directional drilling devices, and as a result, directional deep drilling using conventional directional drilling devices does not correspond to the desired path of the sunk wellbore.
Moreover, another relevant disadvantage of using conventional directional drilling devices is actually caused by the spatial distance of the magnetic field sensors from the head section of the housing; because of the great distance of the magnetic field sensors from the head section, slight deviations of the head section in conventional directional drilling devices in, e.g. three spatial directions are not detected at an early stage, rather, these early deviations in direction can only be identified later by means of the magnetic field sensors located in the base section. Since the deviations in direction are detected only after a certain period of time, subsequent corrections in the directional path of the sunk bore are necessary, and the later the directional deviations of the rotary drill bit are detected, the more time-consuming and costly the corrections of the directional drilling will be. Efforts in the prior art to directional deviations of the head sections of directional drilling devices by installing the magnetic field sensors at least near the head section in conventional directional drilling devices, as described below, have failed due to the significant increase in the occurrence of magnetic declinations with the decrease in the spatial distance of the magnetic field sensors from the head section.